Correct Examples:
* I'd like to enquire about the availability of this product.
* The police are enquiring into the cause of the accident.
* We're enquiring after your health.
* I enquired of the waiter about the specials.
Incorrect Example:
* I enquired the price of the book. (This is incorrect because it's missing a preposition. It should be "I enquired about the price of the book.")
However, there are rare exceptions. In some very specific contexts, "enquire" might be used without a preposition, but it's not common usage.
Example:
* "He enquired deeply into the matter." (In this example, the verb "enquire" could be considered to function as a transitive verb, taking "deeply" as an adverbial modifier and "into the matter" as its direct object. It's still grammatically correct, but it's less common than using a preposition.)
In general, it's safest to use "enquire" with a preposition to ensure clear and correct communication.